Root cause of the Windows worker-thread teardown access violation found via the diagnostic in #380.

The bug

When a task threw a normal exception (or crashed into the IllegalInstruction path), the worker signalled the future twice in php_parallel_scheduler_run():

1. PHP_PARALLEL_ERROR (resp. READY|ERROR) when saving the task error, then
2. an unconditional trailing php_parallel_monitor_set(future->monitor, PHP_PARALLEL_READY) at the end of the function.

Future::value() waits on READY|FAILURE|ERROR, so the first signal already releases the consumer. The consumer can then tear the future down — freeing future->monitor — before the worker reaches the second signal, which then dereferences a dangling monitor inside pthread_cond_signal → use-after-free.

On Windows this is a hard 0xC0000005 (caught here via a diagnostic backtrace):

php_parallel_thread            scheduler.c
 └ php_parallel_scheduler_run  -> monitor_set(future->monitor, PHP_PARALLEL_READY)
    └ php_parallel_monitor_set  monitor.c:93  pthread_cond_signal(&monitor->condition)
       └ <pthreads dll>  -> deref garbage (0x10000000A) -> AV

It surfaced in tests/functional/007.phpt (bootstrap set inside a task). On Linux the freed memory stayed readable, so it went unnoticed; on Windows it was masked by the catch-all VEH from #355.

The fix

The error paths now signal READY|ERROR exactly once and skip the trailing READY (guarded by a ready flag). Once that single monitor_set returns, the worker never touches the future again, closing the window. Setting READY in the error path also keeps the future destructor (which waits for READY) from blocking when value() is never called.

The success and kill paths are unchanged: they have no early wake and still rely on the trailing READY.

Testing

• Linux suite green (148/148).
• Windows CI on this PR should show functional/007 passing for the right reason (no AV).

Related

• Unblocks Narrow the Windows VEH to undefined-function calls only #379 (narrowing the Windows VEH) — 007 will then pass instead of being masked.
• Supersedes the investigation in [DIAGNOSTIC - do not merge] Locate the Windows worker-thread teardown AV #380 (diagnostic, to be closed).